"An egg a day can cut chances of suffering a fatal stroke," The Times reports. A new review of existing data covering around 300,000 people suggests eating up to one egg a day may lower stroke risk; but not the risk of heart disease.

The health effects of eggs have been debated for years. Eggs, which contain cholesterol, were thought to increase risk of heart disease by raising cholesterol levels.

But more recent studies show that cholesterol in food has little impact on the levels of cholesterol in your blood – most cholesterol in the blood is made by the liver.

Researchers wanted to carry out an updated analysis of the evidence on the link between eating eggs and the risk of stroke and heart disease.

The analysis found no link with heart disease and a small reduced risk (12%) of stroke for people who ate around one egg a day, compared to those who ate less than two a week.

The research supports the idea that eggs can be part of a healthy diet. However, it didn't look at people's whole diet, so we don't know what else they were eating, or how the eggs were prepared.

Also, the researchers didn't find that more was better – there was no evidence that people reduced their risk in line with the number of eggs they ate.

Eggs are a good source of protein, vitamins and minerals, so adding one a day to your breakfast could be a healthy way to start the day.

Where did the story come from?

The study was carried out by researchers from the EpidStat Institute in Michigan and DLW Consulting Services in Utah, both in the US, and was funded by the Egg Nutrition Center. This could be seen as a conflict of interest.

The study was published in the peer-reviewed Journal of the American College of Nutrition.

The news was greeted with enthusiasm and little criticism by the UK media. Most reported the study results reasonably accurately.

Both The Sun and the Daily Mirror described the modest 12% drop in relative risk as having "slashed" stroke risk, which is something of an exaggeration.

Although several reports included quotes from the Egg Nutrition Center, none pointed out that the centre had funded the study.

The Egg Nutrition Center is the self-styled "science and nutrition education division" of the American Egg Board (AEB), which is a trade association representing American egg farmers.

The Times' headline stated that eating eggs could cut chances of having a "fatal" stroke, but the study did not find a statistically significant difference in risk of fatal stroke from egg consumption.

What kind of research was this?

A meta-analysis is a good way of summarising the research on a topic; however it's only as good as the studies included. In this case, all were prospective cohort studies.

Cohort studies can find links between factors (egg consumption and heart disease or stroke) but cannot show that one factor causes another.

What did the research involve?

Researchers identified all prospective studies published up to August 2015, which looked at egg consumption by adults and either heart disease or stroke.

They pooled the results and looked to see whether high egg consumption compared to low egg consumption had any effect on these outcomes. They also looked for a "dose response" – a suggestion that risk went up or down in line with the number of eggs people ate each week.

Most of the studies classified high egg consumption as about an egg a day, and low egg consumption as less than two eggs a week.

Most, but not all, adjusted their figures to take account of confounding factors that can affect risk of heart disease and stroke, such as:

weight

age

sex

smoking history

exercise

(in a few cases) how healthy participants' diet was overall

The researchers did standard tests to look for publication bias and to see whether the summary results were overly affected by one or more studies.

What were the basic results?

People whose egg consumption was high were no more or less likely to get heart disease (summary relative risk estimate (SRRE) 0.97; 95% confidence interval (CI) 0.88 to 1.07) than people whose egg consumption was low. This result was based on seven studies including 276,000 people.

However, people who ate an egg per day were 12% less likely to have a stroke than people who ate less than two eggs per week (SRRE 0.88, 95% CI 0.81 to 0.97). This was based on seven studies including 308,000 people.

The researchers found no sign that the stroke risk decreased in proportion to the number of eggs eaten.

How did the researchers interpret the results?

The researchers concluded: "consumption of up to one egg daily may contribute to a decreased risk of total stroke [all types of stroke] and daily egg intake does not appear to be associated with risk of coronary heart disease."

Conclusion

This research broadly supports previous studies in this area, which suggest eating eggs does not increase the chances of getting heart disease or stroke. It raises the possibility that eggs may decrease the risk of having a stroke, but there are limitations to the study, meaning this result may not be reliable.

It's interesting that researchers did not find a "dose response" between stroke risk and the number of eggs eaten. Usually, if something is having an effect on the chances of getting a condition, you can see a linear pattern – having more of that food or treatment increases or decreases chances of the disease, perhaps up to a certain point. But in this case, you can't see any clear pattern.

Studies that identify just one factor – in this case people's egg consumption –without balancing that with information about their overall diet and lifestyle, may find false associations that are actually explained by other factors. For example, people who eat eggs may be more likely to eat a generally healthy diet, or to exercise more, both of which would decrease the chances of stroke.

Another factor to be aware of is that the 12% risk reduction is quite small, and the confidence interval comes fairly close to the point at which the result is no longer statistically significant. This means it is close to the margin of error, so could be down to chance or a blip in the data.

It is important to remember to eat a balanced diet, rather than just assuming one type of food is best. There's a big difference between eating a daily boiled or poached egg with wholegrain toast and spinach, or eating an egg as part of a daily fry-up full of salt and fat.

Over on our Facebook page, some readers had questions about our roundup of employment figures. Where does the unemployment figure of 1.8 million come from, is it a count or an estimate? If it’s an estimate what is the margin of error? The Labour Force Survey figures are estimates, so there is some uncertainty about […]

"Adding fluoride to tap water could save the NHS millions and dramatically improve children's dental health," the Mail Online reports. A new UK study concluded that water fluoridation is a "safe and effective" way of preventing tooth decay in children.

The study used national data to compare the rates of tooth decay and other health outcomes in areas of England where fluoride either has or has not been added to the water.

Primarily, the study seems to confirm what is already well established – fluoride protects against tooth decay. Rates of tooth decay among five and 12-year-olds and hospital admissions for tooth decay in under-fives were significantly lower in water-fluoridated areas.

Whether fluoride could have detrimental effects on other areas of health has been a concern. This study didn't find an adverse effect for any of the outcomes examined. In fact, water fluoridation was linked to small decreases in the rates of bladder cancer and kidney stones, and a tiny reduction in all-cause death. There was also no evidence water fluoridation increased the rates of children born with Down's syndrome.

But we should not automatically assume water fluoridation is protective against bladder cancer, kidney stones and death, as the differences in rates are quite small and could be accounted for by many unmeasured factors.

Overall, the study lends support to the positive effects of water fluoridation on dental health among young children. However, firmer conclusions on possible wider health effects cannot be made.

Where did the story come from?

The study was carried out by researchers from Public Health England (PHE) and was published in the peer-reviewed journal of Community Dentistry and Oral Epidemiology. No sources of financial support are reported.

In the interests of transparency, it should be made clear that Bazian Ltd carried out an independent analysis of key research submitted to South Central Strategic Health Authority as part of the public consultation on the proposal to fluoridate water in Southampton.

The Mail's coverage is generally accurate, though their article focuses on the effects of child tooth decay. It doesn't cover the aim of this research – to look into other health effects – or cover the limitations of the evidence. Saying that "putting fluoride in the water everywhere would save the NHS millions" is only an assumption. The article also doesn't recognise that in some parts of the UK, fluoride naturally occurs at the recommended levels.

What kind of research was this?

This was a cross-sectional study that aimed to look at the association between water fluoridation schemes in England and selected health outcomes.

Six million people in England are said to live in areas where the level of fluoride in water has been adjusted, the main reason being to reduce the public health burden of dental caries. Dental caries, or tooth decay, are reported to affect more than one-quarter of young children, with higher rates in areas of greater deprivation.

Fluoride has long been recognised to reduce the risk of dental caries. Water fluoridation schemes in England (mostly introduced from the late-60s to mid-80s) aim to achieve a level of one part fluoride per million (1ppm) in water, with a maximum permitted level of 1.5ppm.

However, while the dental effects of fluoride are well established, what is less known is whether fluoride could have other detrimental health effects or, conversely, possible health benefits. This study aimed to compare rates of dental and other health outcomes in areas of England with and without water fluoridation.

What did the research involve?

This study used geographical information systems (computer systems used to track and assess data for defined geographical regions) and known patterns of water supply to estimate the level of exposure to fluoridated water in small areas and administrative districts in England.

Fluoride exposure was estimated for small areas (lower super output areas, LSOAs) with a population range of 1,000-3,000, and for administrative districts known as upper tier local authorities (UTLAs) and lower tier local authorities (LTLAs). Areas where the level of fluoride in water naturally reached around 1ppm without added fluoride were excluded.

Health outcomes examined for the regions (and their data source) were as follows:

dental caries at five and 12 years old – National Dental Epidemiology Programme for England

hospital admissions for dental caries in young children aged one to four years – 2012 Annual Report of the Chief Medical Officers

hip fractures – Hospital Episode Statistics (HES) data

kidney stones – HES data

Down's syndrome – National Down syndrome Register

bladder cancer – English Cancer Registration

bone cancer – English Cancer Registration

overall cancer – English Cancer Registration

all-cause death – Office for National Statistics

The time period in which these outcomes were assessed varied for the individual outcome, but was mostly in the 2000s, up to 2010-13.

The associations between water fluoridation and these outcomes were adjusted for potential confounding factors of deprivation and ethnicity. With the exception of child dental caries, other outcomes were also adjusted for age and gender. Down's syndrome was only adjusted for mother's age.

What were the basic results?

Around 1 in 10 of the LSOAs, LTLAs and UTLAs in England have water fluoridation schemes.

Looking at the dental outcomes, water fluoridation was associated with a significant reduction in the odds of child dental caries (28% reduction for five-year-olds and 21% for 12-year-olds). The rate of hospital admission for dental caries was 42 per 100,000 young children in fluoridated areas, compared with 370 in non-fluoridated areas. This was calculated as a 55% risk reduction.

Looking at other health outcomes, three statistically significant associations were found. Water fluoridation was associated with a reduction in the number of cases of bladder cancer and kidney stones (both 8% reduced incidence) and a small reduction in all-cause death (1.3% reduction).

There were no other associations found for any other health outcomes.

How did the researchers interpret the results?

The researchers concluded that: "This study uses the comprehensive data sets available in England to provide reassurance that fluoridation is a safe and highly effective public health measure to reduce dental decay.

"Although lower rates of certain non-dental outcomes were found in fluoridated areas, the ecological, observational design prohibits any conclusions being drawn regarding a protective role of fluoridation."

Conclusion

This cross-sectional study used reliable national data on water fluoridation areas and linked this to registries and databases to see how this influenced the rate of different health outcomes.

Primarily, the study seems to confirm what is already quite well established – fluoride protects against tooth decay. The rate of tooth decay among young children is a particular concern and is a widespread problem across the UK. The study found rates of tooth decay among five and 12-year-olds and hospital admissions for tooth decay in under-fives were significantly lower in fluoridated areas.

The study also aimed to look at whether water fluoridation has any detrimental health effects. It didn't find an adverse effect for any of the outcomes examined. In fact, water fluoridation was associated with decreased rates of bladder cancer and kidney stones. A reduction in all-cause mortality was also found, though this was tiny.

There are, however, important points to keep in mind:

This type of study cannot prove cause and effect. Given the known effect of fluoride on dental health, the reduction in rates of child tooth decay in fluoridated areas could be directly attributed to water fluoridation. But this link is not certain. For other health outcomes – as the researchers rightly acknowledge – you can be less sure. You cannot say from this study that fluoridating water definitely protects against bladder cancer or kidney stones, even less so from mortality risk. The risk decreases are relatively small, and there may be many other factors that account for the differences the study has not been able to examine.

For rates of child tooth decay, data is limited to the National Dental Epidemiology Programme for England, which gives information only for five and 12-year-olds. Though these may be representative, this still does not cover all children. For under-fives, dental health has been assessed through hospital admissions for tooth decay. This would not cover children who may have tooth decay, but are not admitted to hospital for extractions.

The study did not examine an exhaustive list of other health effects. Fluoride may have effects on other areas of health that this study has not examined.

The study examined by water fluoridation area. But there is no certainty that the people living in these areas have always lived here. You don't know about their water exposure in other areas of the UK, or elsewhere.

Even if individuals had always resided in the area assessed, individual exposure could still vary widely. For example, some people could be drinking regular glasses of tap water throughout the day, while others may not.

Also, as the researchers say, they were not able to account for how long the water fluoridation scheme has been in place, which will vary between areas.

Overall, this study lends support to the positive effect of water fluoridation on dental health among young children. However, firmer conclusions on possible wider health effects cannot be made.

In New York the sea will rise by up to two metres.Donald R. Swartz / shutterstock

“Sea-level rise” is a loaded statement and instils concern, scepticism and humour. From a sceptical stand point one could think about your own experience. I have been going to the beach near my parents’ house on the south coast of England for nearly 30 years. In all that time I can’t ever remember paddling in the water and thinking, “gosh, this is higher than it was last year”. Yet, over a similar period of time satellite observations show a global average sea-level rise of around 8cm. In fact a trend has been shown to go back further, to the late 19th and early 20th century.

The record of observations over the past 100 years or so begs the question, will this rise continue? A new study that colleagues and I have published in PNAS looks at what happens to the sea level at 2°C warming and beyond. Our work, led by Svetlana Jevrejeva of the UK’s National Oceanography Centre, shows two key things.

First, that for an emissions scenario that causes global temperature to rise by 2°C and 5°C relative to the global temperature around 1870, there are a range of sea levels projected from 53cm to 178cm above the level in 2000. Second, that while the global average is projected to increase with rising temperatures, sea levels will not increase by the same amount everywhere.

The sea isn’t actually ‘level’

Let’s start with the second point as it will help answer the first. The sea is not level. In fact, it is anything but level. The reason is gravity. The force that keeps your feet firmly on the ground is also acting upon the ocean. The ocean is continually adjusting itself so that its surface – the sea level – feels the same gravitational pull everywhere (called an equipotential surface).

Large things sitting on land, such as ice sheets, are big enough to pull (via their own gravity) the ocean towards them. If bits of an ice sheet or glacier fall off then their ability to pull the ocean towards them is less, so the ocean adjusts, and you have just added water to the ocean that wasn’t in it before which alters the sea level as well.

Greenland’s ice sheet is so big its gravity attracts the ocean.Harvepino/NASA/Shutterstock

This adjustment is happening all the time. Around 20,000 years ago there used to be some enormous ice sheets over North America and Scandinavia, which pushed down the land surface in those places. As the ice sheets melted the land surface rebounded and is still doing so today. Further from where these ice sheets used to be, the land subsided and its still doing so today. And there was the small matter of all that melted ice raising global sea level by about 120m, which was adjusting itself to keep gravity equal across its surface.

Each of the components that contribute to sea level (glaciers, ocean warming, ice sheets and so on) has a unique pattern for how much it will add to sea level in a particular place. If we add them up we get the total sea level at that point and also how much each component has contributed.

The (really really) short result of all this research is that each component shows a range of possible responses to each scenario. By running the computer simulations many times, it appears that certain responses are more likely to happen than others. This allows us to say something about how likely a certain sea-level rise could occur in the future.

This is best shown with an example. Let’s take Jakarta. The Indonesian capital is home to around 12m people, of whom nearly 1.6m live less than 450cm above sea-level.

We’re going to need a lot of sandbags.Nadezda Murmakova/Shutterstock

Our most likely projection for a temperature rise of 5°C is 85cm, which is pretty much the same as the global average. However, we can also think about what all those possible responses of each component are for a 5°C warming. In these situations there is a less than 5% chance of sea level being less than 49cm and less than 5% chance of sea level being more than 180cm.

In the two cases, different components contribute a different amount (remember they each have a unique pattern). In the “lower” projection (49cm) it is ocean warming that dominates, while in the “higher” projection (180cm) it is the Antarctic ice sheet that dominates, followed by not insignificant contributions from ocean warming, glaciers and the Greenland ice sheet.

Of course there are other things going on locally other than these components. For Jakarta, the gravest concern is subsidence. This mega city is sinking, mainly because of groundwater extraction. Projections of subsidence by 2100 for Jakarta are 230-300cm. Put these together with our higher sea level projection and we get 410-480cm of local sea-level rise. Remember the 1.6m people currently who live below 450cm? That number is likely to rise with a growing population.

We started with the phrase “sea-level rise”. It is really important that we unpack this sort of phrase to fully understand what it means. We must recognise the difference between a global number and a local number. For Jakarta, global sea-level is important, but the local sea-level matters too. The sea level is not level – we should accept this fact and embrace the complexity of what makes up rising seas.

Luke Jackson received funding from the European Union's Seventh Programme for Research, Technological Development and Demonstration under Grant Agreement No: FP7-ENV-2013-Two-Stage-603396-RISES-AM. He is currently working on the Climate Econometrics project, funded by the Robertson Foundation (Grant No: 9907422).

Editor, Although the analysis of health and safety regulation in Great Britain is depressingly inaccurate, (Time to take a risk and cut back on red tape – Monday 28 September), Pinstripe will be pleased to hear all of his ‘ideas’ were implemented some time ago. The Health and Safety Executive (HSE) is on target to […]READ MORE

When Spanish prime minister Mariano Rajoy was finally able to announce the formation of a minority government after 10 months of deadlock, he called for political unity. The national parliament must work together to make up for lost time, he said.

But that unity will not easily be achieved while most other political parties are embroiled in their own internal struggles. Rajoy was only able to make his breakthrough thanks to a decision by the Socialist Party (PSOE) to abstain from a vote to allow him to form a government, rather than voting against him. That decision has split the party and led to the resignation of its leader, Pedro Sánchez.

Spain has endured two elections in the past year alone, and Rajoy’s centre-right People’s Party (PP) was the only major party to increase its vote and number of seats between those two votes. Rajoy’s strategists will therefore already be planning their next move.

The PP may be looking to dissolve parliament to call a fresh election. That could happen as early as May 2017 – as soon as is constitutionally possible. Rajoy sees a chance to secure a more stable share of the vote and even to form a majority government. It will not have escaped his attention that the PSOE’s abstention in his investiture vote was linked to its desire to avoid going to the polls at such a moment of weakness.

Socialists in disarray

The current political environment is challenging for social democratic parties all over the world, but the PSOE appears more hapless than most.

Having resigned as party leader at the beginning of October, Sánchez stepped down from parliament altogether on the eve of Rajoy’s successful investiture vote. His departure drew a close to an alarming month of infighting for the socialists.

The caretaker leadership that took over was keen to avoid another election. Given how many votes the party had lost between the elections in December 2015 and June 2016 votes, its position is weak. Its chances of being able to form a government, even in coalition, were slim at best. It would have needed the support of left-wing upstart Podemos and independence-supporting regional parties. That was acceptable to Sánchez, but not to some of his opponents in the party, many of whom were involved in the caretaker leadership.

While the party membership generally backed Sánchez’s stance of voting against Rajoy’s minority government and forcing another election, 68 of the party’s 85 deputies abstained on the orders of the caretaker leadership.

Essentially, the split within the party centred on whether the Socialists should pragmatically acknowledge their own fragility and permit Rajoy to form a government on the basis that his party obtained the most seats in June, or whether, as Sánchez suggested, they should, on principle, vote against a party which has enthusiastically implemented harsh austerity. This while conspicuously failing to address numerous allegations of corruption within its own ranks.

The Podemos problem

Other parties have profited from the PSOE’s plight too. Podemos has wasted no time in proclaiming itself the genuine opposition to the PP government, given the decisive role played by the PSOE in securing Rajoy’s parliamentary endorsement.

Younger voters have been attracted to Podemos because they see both major parties as representing their parents’, or even their grandparents’, interests. Many have still not forgotten the austerity policies introduced by the PSOE when it was last in government under Rodríguez Zapatero.

The new-media-savvy Podemos has been a major beneficiary as austerity has borne down on the young and the poorest in society. Its critique of the status quo is immeasurably more convincing than its policies but party leader Pablo Iglesias’s Manichean approach, based on a reductionist confrontation between “the people” and the corrupt establishment, appeals to many.

Podemos has problems of its own, though. A disappointing performance in the June 2016 election – more than 1 million votes down on the December result – has caused division. Iglesias’ lieutenant Íñigo Errejón has advocated a more measured, pragmatic strategy to reassure voters disquieted by the leader’s often heavy-handed rhetorical spasms.

It remains to be seen whether the PSOE and Podemos are able to find common ground in order to mount a rigorous, yet constructive, opposition capable of holding the new PP government to account.

Paul Kennedy does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond the academic appointment above.

The Conservatives have promised to continue the current freeze in regulated rail fares for the next five years. This means that while those rail fares will still increase, they won’t rise any faster than the Retail Price Index (RPI) measure of inflation. The RPI is statistically flawed, does not meet international standards, and is consequently […]

On a slow news day in the secular world, BBC News has picked up on a survey of teachers in which many report that financial pressure on pupils’ families is having an impact on their learning. The survey was conducted by the NASUWT union. It’s also recently published similar results on unqualified teachers (we’ll be looking at that issue...